Imaging lens

ABSTRACT

An imaging lens includes a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group having negative refractive power, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens having negative refractive power, and a third lens having positive refractive power. The second lens group includes a fourth lens having positive refractive power and a fifth lens having positive refractive power. The third lens group includes a sixth lens and a seventh lens. The first to fifth lenses have specific Abbe&#39;s numbers.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera to be builtin a cellular phone, a portable information terminal, or the like, adigital still camera, a security camera, a vehicle onboard camera, and anetwork camera.

In these years, in place of cellular phones that are intended mainly formaking phone calls, so-called “smartphones”, i.e., cellular phones withfunctions of portable information terminals (PDAs) and/or personalcomputers, have been more widely used. Since the smartphones generallyare highly functional as opposed to the cellular phones, it is possibleto use images taken by a camera thereof in various applications.

Generally speaking, product groups of cellular phones and smartphonesare often composed according to specifications for beginners to advancedusers. Among them, an imaging lens to be mounted in a product designedfor advanced users is required to have a high resolution lensconfiguration so as to be also applicable to a high pixel count imagingelement of these years.

As a method of attaining a high-resolution imaging lens, there is amethod of increasing the number of lenses that compose the imaging lens.However, the increase of the number of lenses easily causes increase ofthe size of the imaging lens. Therefore, the lens configuration having alarge number of lenses is disadvantageous for mounting in a small-sizedcamera such as the above-described cellular phones and smartphones. Forthis reason, an imaging lens has been developed so as to restrain thenumber of lenses as small as possible. However, with rapid advancementin achieving higher pixel count of an imaging element in these days, animaging lens has been developed so as to attain higher resolution ratherthan attaining shorter total track length of the imaging lens. As anexample, there is an advent of a camera unit formed to be able to obtainan image that is equivalent to that obtained by a digital still cameraby attaching the camera unit to a cellular phone or a smartphone, whichis different from a conventional camera unit containing an imaging lensand an imaging element to be mounted inside of a cellular phone or asmartphone.

In case of a lens configuration composed of seven lenses, since thenumber of lenses that compose an imaging lens is many, it is somewhatdisadvantageous for downsizing of the imaging lens. However, since thereis high flexibility in designing, it has potential of attainingsatisfactory correction of aberrations and downsizing in a balancedmanner. For example, as an imaging lens having a seven-lensconfiguration as described above, an imaging lens described in PatentReference is known.

Patent Reference: Japanese Patent Application Publication No.2012-155223

The imaging lens described in Patent Reference includes a first lenshaving a biconvex shape, a second lens that is joined to the first lensand has a biconcave shape, a third lens that is negative and has a shapeof a meniscus lens directing a convex surface thereof to an object side,a fourth lens that is positive and has a shape of a meniscus lensdirecting a concave surface thereof to the object side, a fifth lensthat is negative and has a shape of a meniscus lens directing a convexsurface thereof to the object side, a sixth lens having a biconvexshape, and a seventh lens having a biconcave shape, arranged in theorder from the object side. According to the imaging lens of PatentReference, by restraining a ratio between a focal length of a first lensgroup composed of the first lens to the fourth lens and a focal lengthof a second lens group composed of the fifth lens to the seventh lenswithin a certain range, it is possible to attain downsizing of theimaging lens and satisfactory correction of aberrations.

The imaging lens described in Patent Reference is small-sized, butaberrations on an image plane are not sufficiently corrected andespecially distortion is relatively large. Therefore, there is a limitby itself in achieving a high-resolution imaging lens. According to thelens configuration of Patent Reference, it is difficult to attainsatisfactory correction of aberrations while downsizing the imaginglens.

Here, such a problem is not specific to the imaging lens to be mountedin cellular phones and smartphones. Rather, it is a common problem evenfor an imaging lens to be mounted in a relatively small camera such asdigital still cameras, portable information terminals, security cameras,vehicle onboard cameras, and network cameras.

In view of the above-described problems in conventional techniques, anobject of the present invention is to provide an imaging lens that canattain downsizing thereof and satisfactory aberration correction.

Further objects and advantages of the present invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the present invention, an imaging lens includes a first lensgroup having positive refractive power; a second lens group havingpositive refractive power; and a third lens group having negativerefractive power, arranged in the order from an object side to an imageplane side. The first lens group includes a first lens having positiverefractive power, a second lens having negative refractive power, and athird lens having positive refractive power. The second lens groupincludes a fourth lens having positive refractive power and a fifth lenshaving positive refractive power. The third lens group includes a sixthlens and a seventh lens.

According to the first aspect of the present invention, when the firstlens has an Abbe's number νd1, the second lens has an Abbe's number νd2,the third lens has an Abbe's number νd3, the fourth lens has an Abbe'snumber νd4, and the fifth lens has an Abbe's number νd5, the imaginglens of the present invention satisfies the following conditionalexpressions (1) to (5):

40<νd1<75  (1)

20<νd2<35  (2)

40<νd3<75  (3)

40<νd4<75  (4)

20<νd5<35  (5)

According to the first aspect of the present invention, the imaging lensincludes the first lens group having positive refractive power, thesecond lens group having positive refractive power, and the third lensgroup having negative refractive power, arranged in the order from theobject side. The refractive powers of the respective lens groups arearranged in the order of “positive-positive-negative” from the objectside. Generally speaking, a chromatic aberration is corrected by acombination of a lens group having positive refractive power and a lensgroup having negative refractive power, arranged in the order from theobject side. According to the lens configuration, in order to attaindownsizing of the imaging lens, it is necessary to increase therefractive power of the positive lens group arranged on the object side.However, when the lens group having positive refractive power has strongrefractive power, it is often difficult to satisfactorily correct achromatic aberration.

According to the first aspect of the present invention, in the imaginglens, the positive refractive power of the whole lens system is sharedbetween the first lens group and the second lens group. Therefore, incomparison with a case where there is only one lens group that haspositive refractive power, the refractive powers of the positive lensesthat compose the respective lens groups are kept relatively weak.Therefore, according to the imaging lens of the present invention, it ispossible to satisfactorily correct aberrations, especially the chromaticaberration. In addition, it is also possible to obtain satisfactoryimage-forming performance that is necessary for high-resolution imaginglens. Moreover, according to the imaging lens of the present invention,since the third lens group has negative refractive power, it is possibleto suitably attain downsizing of the imaging lens.

The first lens group includes three lenses, such that the refractivepowers of those lenses are arranged in the order ofpositive-negative-positive. Those three lenses are respectively madefrom lens materials that satisfy the conditional expressions (1) to (3).With the arrangement of the refractive powers and the order of theAbbe's numbers of the respective lenses, it is possible to suitablyrestrain generation of chromatic aberration in the first lens group andalso satisfactorily correct the chromatic aberration if generated.

Furthermore, according to the first aspect of the present invention, inthe imaging lens, the second lens group includes two positive lenses andis composed of a combination of a lens made of a high-dispersionmaterial and a lens made of a low-dispersion material so as to satisfythe conditional expressions (4) and (5). Therefore, it is possible tofurther satisfactorily correct aberrations generated in the first lensgroup, especially chromatic aberration.

Generally speaking, in order to attain high-resolution imaging lens, itis necessary to satisfactorily correct aberrations, especially chromaticaberration. According to the imaging lens of the present invention, withthe arrangement of the refractive powers of the respective lens groupsof the first lens group to the third lens group, the arrangement of therefractive powers and the order of the Abbe's numbers of the threelenses that compose the first lens group, and the order of the Abbe'snumbers of the two positive lenses that compose the second lens group,it is possible to more satisfactorily correct the chromatic aberrationthan a conventional imaging lens.

According to a second aspect of the present invention, the sixth lensand the seventh lens have both a negative refractive power. When thesixth lens has an Abbe's number νd6 and the seventh lens has an Abbe'snumber νd7, the imaging lens having the above-described configurationpreferably satisfies the following conditional expressions (6) and (7):

20<νd6<35  (6)

40<νd7<75  (7)

According to the second aspect of the present invention, in the imaginglens, the third lens group includes two negative lenses and is composedof a combination of a lens made of a low-dispersion material and a lensmade of a high-dispersion material so as to satisfy the conditionalexpressions (6) and (7). Therefore, it is possible to moresatisfactorily correct aberrations, especially the chromatic aberration,generated in the first lens group and the second lens group.

According to a third aspect of the present invention, when the firstlens has a focal length f1 and the third lens has a focal length f3, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (8):

0.3<f3/f1<3.0  (8)

When the imaging lens satisfies the conditional expression (8), it isachievable to satisfactorily correct astigmatism and a field curvature,while attaining a small size of the imaging lens. When the value exceedsthe upper limit of “3.0”, the third lens has weak positive refractivepower in the first lens group. Therefore, in order to correctaberrations, it is necessary to increase the positive refractive powerof the first lens that has positive refractive power similarly to thethird lens.

In this case, although it is advantageous for downsizing of the imaginglens, a back focal length is short, so that it is difficult to securespace to dispose an insert such as an infrared cutoff filter. Moreover,in the astigmatism, a sagittal image surface tilts toward a side of animage plane (a plus side). Therefore, the periphery of the image curvesto a side of the image plane, and it is difficult to obtain satisfactoryimaging performance. On the other hand, when the value is below thelower limit of “0.3”, although it is advantageous for securing the backfocal length, it is difficult to downsize the imaging lens.

In addition, a tangential image surface curves to the object side (aminus side) at the periphery of the image. Therefore, an astigmaticdifference increases and also in this case, it is difficult to obtainsatisfactory image-forming performance.

According to a fourth aspect of the present invention, when the secondlens has a focal length f2 and the third lens has a focal length f3, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (9):

−3.0<f2/f3<−0.3  (9)

When the imaging lens satisfies the conditional expression (9), it isachievable to restrain the chromatic aberration, the field curvature,and the astigmatism within respective preferred ranges in a balancedmanner, while downsizing the imaging lens. When the value exceeds theupper limit of “−0.3”, the second lens has strong negative refractivepower relative to the positive refractive power of the third lens.Therefore, although it is advantageous for securing the back focallength and correcting an axial chromatic aberration, it is difficult todownsize the imaging lens.

In addition, an image-forming surface curves to the image plane side atthe periphery of the image, so that the field curvature is excessivelycorrected and the astigmatic difference increases. Therefore, it isdifficult to obtain satisfactory image-forming performance. On the otherhand, when the value is below the lower limit of “−3.0”, although it isadvantageous for downsizing of the imaging lens, it is difficult tosecure the back focal length. Moreover, the astigmatic differenceincreases, and the image-forming surface curves to the object side atthe periphery of the image and the field curvature is insufficientlycorrected.

In addition, the axial chromatic aberration and a chromatic aberrationof magnification also respectively increase. Therefore, also in thiscase, it is difficult to obtain satisfactory image-forming performance.

According to a fifth aspect of the present invention, when the wholelens system has a focal length f and the fourth lens has a focal lengthf4, the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (10):

4.5<f4/f<9.0  (10)

When the imaging lens satisfies the conditional expression (10), it isachievable to restrain the curving of the image-forming surface whilesatisfactorily correcting the axial chromatic aberration. When the valueexceeds the upper limit of “9.0”, the fourth lens has weak positiverefractive power relative to the refractive power of the whole lenssystem. As a result, it is easier to correct the axial chromaticaberration. However, since the tangential image surface curves at theperiphery of the image, it is difficult to restrain the curving of theimage-forming surface. On the other hand, when the value is below thelower limit of “4.5”, the fourth lens has strong positive refractivepower relative to the refractive power of the whole lens system.

Therefore, the focal length of the whole lens system is short, and it isdifficult to secure the back focal length. Here, when the fourth lenshas strong refractive power like this, if the refractive power ofanother lens having positive refractive power is weakened or therefractive power of other lens having negative refractive power isincreased so as to restrain shortening of the focal length, theastigmatic difference increases. Therefore, it is difficult to restrainthe curving of the image-forming surface.

According to a sixth aspect of the present invention, when the wholelens system has a focal length f and a composite focal length of thefourth lens and the fifth lens is f45, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (11):

1.5<f45/f<5.0  (11)

When the imaging lens satisfies the conditional expression (11), it isachievable to satisfactorily correct the field curvature and theastigmatism, while downsizing the imaging lens. When the value exceedsthe upper limit of “5.0”, the second lens group has weak positiverefractive power relative to the refractive power of the whole lenssystem. Therefore, in order to correct aberrations, it is necessary toincrease the positive refractive power of the first lens group. As aresult, although it is advantageous for correcting the astigmatism andfor downsizing of the imaging lens, it is difficult to secure the backfocal length.

Moreover, since the image-forming surface curves to the image planeside, it is difficult to obtain satisfactory image-forming performance.Here, when trying to correct the aberrations by weakening the negativerefractive power of the third lens group for the weakening of thepositive refractive power of the second lens group, although it isadvantageous for correcting the chromatic aberration of magnification,the astigmatic difference increases. Therefore, it is difficult toobtain satisfactory image-forming performance. On the other hand, whenthe value is below the lower limit of “1.5”, the second lens group hasstrong positive refractive power relative to the refractive power of thewhole lens system. Therefore, the astigmatic difference increases, andit is difficult to obtain satisfactory image-forming performance.

According to a seventh aspect of the present invention, when a compositefocal length of the fourth lens and the fifth lens is f45 and acomposite focal length of the sixth lens and the seventh lens is f67,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (12):

−6.0<f45/f67<−1.5  (12)

When the imaging lens satisfies the conditional expression (12), it ispossible to satisfactorily correct the chromatic aberration and theastigmatism, while downsizing the imaging lens. Moreover, when theimaging lens satisfies the conditional expression (12), it is alsopossible to restrain an incident angle of a light beam emitted from theimaging lens to an image plane of an imaging element. As is well known,an imaging element such as a CCD sensor or a CMOS sensor has a so-calledchief ray angle (CRA) set in advance, i.e. a range of an incident angleof a light beam that can be taken in the sensor. By restraining theincident angle of a light beam emitted from the imaging lens to theimage plane within the range of CRA, it is possible to suitably restraingeneration of shading, which is a phenomenon of becoming dark on theimage periphery.

When the value exceeds the upper limit of “−1.5” in the conditionalexpression (12), it is easy to restrain the incident angle of a lightbeam emitted from the imaging lens to the image plane within the rangeof CRA, and it is also easy to secure the back focal length. However, atthe same time, it is difficult to downsize the imaging lens. Moreover,in the astigmatism, the sagittal image surface curves to the image planeside, so that it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof “−6.0”, although it is advantageous for downsizing of the imaginglens, it is difficult to secure the back focal length. In addition, itis also difficult to restrain the incident angle of a light beam emittedfrom the imaging lens to the image plane within the range of CRA.Moreover, in the astigmatism, the tangential image surface curves to theobject side. Therefore, the astigmatic difference increases, and it isdifficult to obtain satisfactory image-forming performance.

According to an eighth aspect of the present invention, when the wholelens system has a focal length f and a distance on the optical axisbetween the third lens and the fourth lens is D34, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (13):

0.05<D34/f<0.3  (13)

When the imaging lens satisfies the conditional expression (13), it ispossible to satisfactorily correct the astigmatism and the distortion,while restraining the incident angle of a light beam emitted from theimaging lens to the image plane of the imaging element within the rangeof CRA. When the value exceeds the upper limit of “0.3”, it is difficultto restrain the incident angle of a light beam emitted from the imaginglens to the image plane within the range of CRA. Moreover, in theastigmatism, the sagittal image surface curves to the image plane side.Therefore, the astigmatic difference increases, and the field curvatureis excessively corrected. For this reason, it is difficult to obtainsatisfactory image-forming performance.

On the other hand, when the value is below the lower limit of “0.05”,although it is easy to restrain the incident angle of a light beamemitted from the imaging lens to the image plane within the range ofCRA, a minus distortion increases. Moreover, in the astigmatism, thesagittal image surface curves to the object side. Also in this case, itis difficult to obtain satisfactory image-forming performance.

According to a ninth aspect of the present invention, when the wholelens system has a focal length f and a distance on the optical axisbetween the fifth lens and the sixth lens is D56, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (14):

0.05<D56/f<0.25  (14)

When the imaging lens satisfies the conditional expression (14), it ispossible to satisfactorily correct the chromatic aberration and thedistortion, while restraining the incident angle of a light beam emittedfrom the imaging lens to the image plane of the imaging element withinthe range of CRA. When the value exceeds the upper limit of “0.25”, aplus distortion increases and a chromatic aberration of magnificationincreases at the periphery of the image, so that it is difficult toobtain satisfactory image-forming performance. Moreover, in this case,it is difficult to secure the back focal length, and it is difficult torestrain the incident angle of a light beam emitted from the imaginglens to the image plane of the imaging element within the range of CRA.On the other hand, when the value is below the lower limit of “0.05”, itis easy to secure the back focal length and it is easy to restrain theincident angle of a light beam emitted from the imaging lens to theimage plane of the imaging element within the range of CRA. However, aminus distortion increases, so that it is difficult to obtainsatisfactory image-forming performance.

According to a tenth aspect of the present invention, when the wholelens system has a focal length f and the seventh lens has a focal lengthf7, the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (15):

−4.0<f7/f<−1.0  (15)

When the imaging lens satisfies the conditional expression (15), it ispossible to restrain the field curvature, the astigmatism, and thechromatic aberration within respective preferable ranges in a balancedmanner. When the value exceeds the upper limit of “−1.0”, the seventhlens has strong negative refractive power relative to the refractivepower of the whole lens system. Therefore, the astigmatic differenceincreases and the image-forming surface curves to the image plane side,so that the field curvature is excessively corrected. In addition, thechromatic aberration of magnification increases at the image periphery,so that it is difficult to obtain satisfactory image performance.

On the other hand, when the value is below the lower limit of “−4.0”,the seventh lens has weak negative refractive power relative to therefractive power of the whole lens system. Therefore, the axialchromatic aberration is insufficiently corrected (a focal position at ashort wavelength moves to the object side relative to a focal positionat a reference wavelength), and it is difficult to obtain satisfactoryimage-forming performance. In this case, it is also difficult to correctthe astigmatism.

According to the imaging lens having the above-described configuration,the sixth lens and the seventh lens are preferably formed as asphericshapes such that their positive refractive powers become stronger fromthe optical axis toward the lens peripheries.

The sixth lens and the seventh lens, which compose the third lens group,are formed as aspheric shapes such that the positive refractive powersbecome stronger from the optical axis toward the lens peripheries. As aresult, it is possible to satisfactorily correct not only the axialchromatic aberration, but also the off-axis chromatic aberration ofmagnification. In addition, it is also possible to suitably restrain theincident angle of a light beam emitted from the imaging lens to theimage plane.

According to the imaging lens of the present invention, it is possibleto provide a small-sized imaging lens that is especially suitable formounting in a small-sized camera, while having high resolution withsatisfactory correction of aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of thepresent invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 according to the embodiment of thepresent invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 according to the embodiment of thepresent invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 according to the embodiment ofthe present invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 according to the embodiment ofthe present invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13;

FIG. 16 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 6 according to the embodiment ofthe present invention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16; and

FIG. 18 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, 13, and 16 are schematic sectional views of theimaging lenses in Numerical Data Examples 1 to 6 according to theembodiment, respectively. Since the imaging lenses in those NumericalData Examples have the same basic configuration, the lens configurationof the embodiment will be described with reference to the illustrativesectional view of Numerical Data Example 1.

As shown in FIG. 1, according to the embodiment, the imaging lensincludes a first lens group G1 having positive refractive power, asecond lens group G2 having positive refractive power, and a third lensgroup G3 having negative refractive power, arranged in the order from anobject side to an image plane side. Between the third lens group G3 andan image plane IM of an imaging element, there is provided a filter 10.The filter 10 is omissible.

The first lens group G1 includes a first lens L1 having positiverefractive power, an aperture stop ST, a second lens L2 having negativerefractive power, and a third lens L3 having positive refractive power,arranged in the order from the object side.

The first lens L1 is formed in a shape such that a curvature radius r1of an object-side surface thereof is positive and a curvature radius r2of an image plane-side surface thereof is negative, so as to have ashape of a biconvex lens near an optical axis X. The shape of the firstlens L1 is not limited to the one of Numerical Data Example 1. The shapeof the first lens L1 can be any as long as the curvature radius r1 ofthe object-side surface thereof is positive. Therefore, the first lensL1 can be formed in a shape such that the curvature radius r2 of theimage plane-side surface thereof is positive, i.e., a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. Numerical Data Examples 2, 3, and 5 are examples, inwhich the first lens L1 has a shape of a meniscus lens that directs aconvex surface thereof to the object side near the optical axis X.

The second lens L2 is formed in a shape such that a curvature radius r4of an object-side surface thereof and a curvature radius r5 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. Here, the shape of the second lens L2 is not limitedto the one in Numerical Data Example 1. The shape of the second lens L2can be any as long as the curvature radius r5 of the image plane-sidesurface thereof is positive. Therefore, the second lens L2 can be formedin a shape such that the curvature radius r4 of the object-side surfacethereof is negative, i.e., a shape of a biconcave lens near the opticalaxis X.

The third lens L3 is formed in a shape such that a curvature radius r6of an object-side surface thereof is positive and a curvature radius r7of an image plane-side surface thereof is negative, so as to have ashape of a biconvex lens near the optical axis X. The shape of the thirdlens L3 is not limited to the one in Numerical Data Example 1. The shapeof the third lens L3 can be any as long as the curvature radius r6 ofthe object-side surface thereof is positive. The third lens L3 can beformed in a shape such that the curvature radius r7 of the imageplane-side surface thereof is positive, i.e., a shape of a meniscus lensdirecting a convex surface thereof to the object side near the opticalaxis X. Numerical Data Example 4 is an example, in which the third lensL3 has a shape of a meniscus lens directing a convex surface thereof tothe object side near the optical axis X.

The second lens group G2 includes a fourth lens L4 having positiverefractive power and a fifth lens L5 having positive refractive power,arranged in the order from the object side. In the second lens group G2,the fourth lens L4 is formed in a shape such that a curvature radius r8of an object-side surface thereof and a curvature radius r9 of an imageplane-side surface thereof are both negative, so as to have a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X.

The fifth lens L5 is formed in a shape such that a curvature radius r10of an object-side surface thereof and a curvature radius r11 of an imageplane-side surface thereof are both negative, so as to have a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. Here, the shape of the fifth lens L5 is notlimited to the one in Numerical Data Example 1. The shape of the fifthlens L5 can be any as long as the curvature radius r11 of the imageplane-side surface thereof is negative. Therefore, the fifth lens L5 canbe formed in a shape such that the curvature radius r10 of theobject-side surface thereof is positive, i.e., a shape of a biconvexlens near the optical axis X. Numerical Data Example 2 is an example, inwhich the fifth lens L5 has a shape of a biconvex lens near the opticalaxis X.

The third lens group G3 includes a sixth lens L6 having negativerefractive power and a seventh lens L7 having negative refractive power,arranged in the order from the object side. The sixth lens L6 is formedin a shape such that a curvature radius r12 of an object-side surfacethereof and a curvature radius r13 of an image plane-side surfacethereof are both positive, so as to have a shape of a meniscus lensdirecting a convex surface thereof to the object side near the opticalaxis X. In addition, the seventh lens L7 is formed in a shape such thata curvature radius r14 of an object-side surface thereof and a curvatureradius r15 of an image plane-side surface thereof are both positive, soas to have a shape of a meniscus lens directing a convex surface thereofto the object side near the optical axis X.

The sixth lens L6 and the seventh lens L7 have the object-side surfacesand the image plane-side surfaces that are formed as aspheric shapeshaving inflexion points. In addition, the sixth lens L6 and the seventhlens L7 are formed in shapes such that their positive refractive powersbecome stronger from the optical axis X toward the lens peripheries.With such shapes of the sixth lens L6 and the seventh lens L7, it isachievable to satisfactorily correct the off-axis chromatic aberrationof magnification as well as the axial chromatic aberration. Moreover, itis also achievable to suitably restrain the incident angle of a lightbeam emitted from the imaging lens to the image plane IM within therange of chief ray angle (CRA).

Here, according to the imaging lens in Numerical Data Example 1, thesixth lens L6 and the seventh lens L7 have the object-side surfaces andthe image plane-side surfaces both of which are formed as asphericshapes having inflexion points. However, it is not necessary to form theboth surfaces as aspheric shapes having inflexion points. Even if onlyone of those surfaces is formed as an aspheric shape having an inflexionpoint, it is still possible to form one or both of those lenses suchthat the positive refractive power(s) become(s) stronger from theoptical axis X toward the lens periphery/peripheries. Moreover,depending on required optical performance and the level of downsizing ofthe imaging lens, it may not be necessary to provide an inflexion pointon the sixth lens L6 and the seventh lens L7.

According to the embodiment, the imaging lens satisfies the followingconditional expressions (1) to (15):

40<νd1<75  (1)

20<νd2<35  (2)

40<νd3<75  (3)

40<νd4<75  (4)

20<νd5<35  (5)

20<νd6<35  (6)

40<νd7<75  (7)

0.3<f3/f1<3.0  (8)

−3.0<f2/f3<−0.3  (9)

4.5<f4/f<9.0  (10)

1.5<f45/f<5.0  (11)

−6.0<f45/f67<−1.5  (12)

0.05<D34/f<0.3  (13)

0.05<D56/f<0.25  (14)

−4.0<f7/f<−1.0  (15)

In the above conditional expressions:

νd1: Abbe's number of a first lens L1νd2: Abbe's number of a second lens L2νd3: Abbe's number of a third lens L3νd4: Abbe's number of a fourth lens L4νd5: Abbe's number of a fifth lens L5νd6: Abbe's number of a sixth lens L6νd7: Abbe's number of a seventh lens L7f: Focal length of a whole lens systemf1: Focal length of the first lens L1f2: Focal length of the second lens L2f3: Focal length of the third lens L3f4: Focal length of the fourth lens L4f7: Focal length of the seventh lens L7f45: Composite focal length of the fourth lens L4 and the fifth lens L5f67: Composite focal length of the sixth lens L6 and the seventh lens L7D34: Distance on the optical axis X between the third lens L3 and thefourth lens L4D56: Distance on the optical axis X between the fifth lens L5 and thesixth lens L6

According to the embodiment, in order to more satisfactorily correctaberrations, the imaging lens satisfies the following conditionalexpression (16):

0.7<f6/f7<1.4  (16)

When the imaging lens satisfies the conditional expression (16), it isachievable to satisfactorily correct the distortion while restrainingthe incident angle of a light beam emitted from the imaging lens to theimage plane IM within the range of CRA. When the value exceeds the upperlimit of “1.4”, although it is easy to restrain the incident angle of alight beam emitted from the imaging lens to the image plane IM withinthe range of CRA, the seventh lens L7 near the image plane IM hasstronger refractive power than the refractive power of the sixth lensL6. Therefore, the distortion in the minus direction increases, and itis difficult to obtain satisfactory image-forming performance. On theother hand, when the value is below the lower limit of “0.7”, thedistortion in the plus direction increases, so that it is difficult toobtain satisfactory image-forming performance. Moreover, it is difficultto restrain the incident angle of a light beam emitted from the imaginglens to the image plane IM within the range of CRA.

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expression when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, all lens surfaces are formed as an aspheric surface.When the aspheric shapes applied to the lens surfaces have an axis Z ina direction of the optical axis X, a height H in a directionperpendicular to the optical axis X, a conic constant k, and asphericcoefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, and A₁₆, the aspheric shapes ofthe lens surfaces are expressed as follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F-number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance on the optical axis between lenssurfaces (surface spacing), nd represents a refractive index, and νdrepresents an Abbe's number, respectively. Here, aspheric surfaces areindicated with surface numbers i affixed with * (asterisk).

Numerical Data Example 1

Basic data are shown below.

f=11.91 mm, Fno=2.9, ω=27.1°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 4.9331.070 1.5346 56.1 (=νd1)  2* −930.893 −0.035    3 (Stop) ∞ 0.112  4*18.923 0.311 1.6355 24.0 (=νd2)  5* 5.803 0.113  6* 9.618 1.053 1.534656.1 (=νd3)  7* −26.477 1.108 (=D34)  8* −4.816 1.452 1.5346 56.1 (=νd4) 9* −4.880 0.100 10* −20.892 1.258 1.6355 24.0 (=νd5) 11* −16.143 1.269(=D56) 12* 10.109 1.086 1.6355 24.0 (=νd6) 13* 5.202 0.858 14* 6.1281.015 1.5346 56.1 (=νd7) 15* 3.566 0.700 16 ∞ 0.300 1.5168 64.2 17 ∞1.693 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −2.258E−03, A₆ = −1.716E−04, A₈ = −8.402E−05, A₁₀ = 7.188E−06, A₁₂ =−1.727E−07, A₁₄ = −5.544E−08, A₁₆ = −4.827E−09 Second Surface k = 0.000,A₄ = 1.813E−02, A₆ = −1.657E−02, A₈ = 5.660E−03, A₁₀ = −9.632E−04, A₁₂ =3.919E−05, A₁₄ = 9.322E−06, A₁₆ = −9.282E−07 Fourth Surface k = 0.000,A₄ = 2.004E−02, A₆ = −2.109E−02, A₈ = 7.483E−03, A₁₀ = −1.366E−03, A₁₂ =7.946E−05, A₁₄ = 1.008E−05, A₁₆ = −1.275E−06 Fifth Surface k = 0.000, A₄= 1.328E−02, A₆ = −1.197E−02, A₈ = 2.756E−03, A₁₀ = −3.323E−04, A₁₂ =9.334E−06, A₁₄ = 1.543E−06, A₁₆ = 6.238E−09 Sixth Surface k = 0.000, A₄= 1.412E−02, A₆ = −7.356E−03, A₈ = 1.464E−03, A₁₀ = −1.635E−04, A₁₂ =9.896E−06, A₁₄ = 3.578E−07, A₁₆ = −7.427E−08 Seventh Surface k = 0.000,A₄ = −4.229E−03, A₆ = −6.810E−04, A₈ = 2.136E−04, A₁₀ = −1.640E−05, A₁₂= −8.553E−07, A₁₄ = −3.664E−07, A₁₆ = 1.570E−08 Eighth Surface k =0.000, A₄ = −7.525E−03, A₆ = 4.344E−04, A₈ = 1.460E−04, A₁₀ =−4.222E−05, A₁₂ = −2.416E−07, A₁₄ = 2.207E−07, A₁₆ = 2.681E−08 NinthSurface k = 0.000, A₄ = −1.153E−03, A₆ = 4.237E−04, A₈ = −3.266E−06, A₁₀= 1.184E−06, A₁₂ = −1.703E−06, A₁₄ = 6.357E−08, A₁₆ = 2.051E−08 TenthSurface k = 0.000, A₄ = −2.682E−03, A₆ = −4.429E−04, A₈ = −8.312E−05,A₁₀ = 2.024E−06, A₁₂ = −9.278E−07, A₁₄ = −1.690E−08, A₁₆ = 5.362E−09Eleventh Surface k = 0.000, A₄ = −2.770E−03, A₆ = −5.065E−04, A₈ =7.597E−06, A₁₀ = −1.210E−06, A₁₂ = 3.920E−08, A₁₄ = 4.009E−09, A₁₆ =−4.901E−11 Twelfth Surface k = 0.000, A₄ = −7.263E−03, A₆ = −2.582E−06,A₈ = −1.576E−06, A₁₀ = 3.658E−07, A₁₂ = 1.955E−08, A₁₄ = 6.544E−10, A₁₆= −1.041E−10 Thirteenth Surface k = 0.000, A₄ = −7.953E−03, A₆ =1.117E−04, A₈ = 1.769E−06, A₁₀ = −1.619E−07, A₁₂ = 1.220E−09, A₁₄ =−7.531E−11, A₁₆ = 1.176E−12 Fourteenth Surface k = 0.000, A₄ =−1.499E−02, A₆ = 4.386E−04, A₈ = 4.879E−07, A₁₀ = 1.022E−07, A₁₂ =−2.511E−09, A₁₄ = −4.879E−10, A₁₆ = 6.044E−12 Fifteenth Surface k =−5.275, A₄ = −7.965E−03, A₆ = 3.077E−04, A₈ = −7.619E−06, A₁₀ =1.795E−07, A₁₂ = 8.605E−09, A₁₄ = −5.893E−10, A₁₆ = 8.607E−12f1=9.18 mmf2=−13.29 mmf3=13.33 mmf4=99.43 mmf5=101.31 mmf6=−18.45 mmf7=−18.52 mmf45=48.43 mmf67=−8.78 mmThe values of the respective conditional expressions are as follows:f3/f1=1.45f2/f3=−1.00f4/f=8.35f45/f=4.07f45/f67=−5.51D34/f=0.09D56/f=0.11f7/f=−1.55f2/f1=−1.45f6/f7=1.00

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 13.36 mm, and downsizing ofthe imaging lens is attained.

FIG. 2 shows a lateral aberration that corresponds to a ratio H of eachimage height to the maximum image height (hereinafter referred to as“image height ratio H”), which is divided into a tangential directionand a sagittal direction (The same is true for FIGS. 5, 8, 11, 14, and17), in the imaging lens of Numerical Data Example 1. Furthermore, FIG.3 shows a spherical aberration (mm), astigmatism (mm), and a distortion(%), respectively, of the imaging lens of Numerical Data Example 1. Inthe lateral aberration diagrams and spherical aberration diagrams,aberrations at each wavelength, i.e. a g line (435.84 nm), an e line(546.07 nm), and a C line (656.27 nm) are indicated. In the astigmatismdiagram, an aberration on a sagittal image surface S and an aberrationon a tangential image surface T are respectively indicated (The same istrue for FIGS. 6, 9, 12, 15, and 18). As shown in FIGS. 2 and 3,according to the imaging lens of Numerical Data Example 1, theaberrations are satisfactorily corrected.

Numerical Data Example 2

Basic data are shown below.

f=11.12 mm, Fno=2.4, ω=28.7°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 5.6722.085 1.5346 56.1 (=νd1)  2* 13.631 −0.0003  3 (Stop) ∞ 0.105  4* 40.1820.382 1.6355 24.0 (=νd2)  5* 6.117 0.049  6* 5.905 0.762 1.5346 56.1(=νd3)  7* −38.291 0.990 (=D34)  8* −3.431 0.350 1.5346 56.1 (=νd4)  9*−3.240 0.108 10* 84.917 0.616 1.6355 24.0 (=νd5) 11* −58.992 1.736(=D56) 12* 7.052 1.350 1.6355 24.0 (=νd6) 13* 4.789 1.526 14* 4.9481.105 1.5346 56.1 (=νd7) 15* 3.686 0.680 16 ∞ 0.300 1.5168 64.2 17 ∞1.414 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −1.916E−03, A₆ = −2.614E−04, A₈ = −4.202E−05, A₁₀ = 9.800E−06, A₁₂ =−5.793E−07, A₁₄ = −1.528E−07, A₁₆ = 1.302E−08 Second Surface k = 0.000,A₄ = 1.459E−02, A₆ = −1.720E−02, A₈ = 5.644E−03, A₁₀ = −9.641E−04, A₁₂ =4.106E−05, A₁₄ = 9.797E−06, A₁₆ = −9.797E−07 Fourth Surface k = 0.000,A₄ = 2.300E−02, A₆ = −2.066E−02, A₈ = 7.394E−03, A₁₀ = −1.370E−03, A₁₂ =8.034E−05, A₁₄ = 1.017E−05, A₁₆ = −1.197E−06 Fifth Surface k = 0.000, A₄= 1.452E−02, A₆ = −1.176E−02, A₈ = 2.846E−03, A₁₀ = −3.407E−04, A₁₂ =7.751E−06, A₁₄ = 1.645E−06, A₁₆ = 4.227E−08 Sixth Surface k = 0.000, A₄= 9.445E−03, A₆ = −7.185E−03, A₈ = 1.433E−03, A₁₀ = −1.523E−04, A₁₂ =1.116E−05, A₁₄ = 2.227E−07, A₁₆ = −1.217E−07 Seventh Surface k = 0.000,A₄ = −1.799E−03, A₆ = −3.115E−04, A₈ = 1.941E−04, A₁₀ = −1.459E−05, A₁₂= −3.805E−07, A₁₄ = −4.646E−07, A₁₆ = −5.256E−08 Eighth Surface k =0.000, A₄ = −1.097E−02, A₆ = 1.037E−03, A₈ = 2.046E−04, A₁₀ =−3.179E−05, A₁₂ = 9.872E−07, A₁₄ = 3.226E−07, A₁₆ = 2.150E−08 NinthSurface k = 0.000, A₄ = −2.374E−04, A₆ = 7.402E−04, A₈ = 6.618E−05, A₁₀= 9.578E−06, A₁₂ = −8.457E−07, A₁₄ = 1.366E−07, A₁₆ = 3.483E−08 TenthSurface k = 0.000, A₄ = 8.502E−05, A₆ = −6.845E−04, A₈ = −3.961E−05, A₁₀= 7.821E−06, A₁₂ = −3.182E−07, A₁₄ = −2.580E−08, A₁₆ = −1.121E−08Eleventh Surface k = 0.000, A₄ = −3.546E−03, A₆ = −1.316E−04, A₈ =−5.946E−06, A₁₀ = −1.087E−06, A₁₂ = 8.261E−09, A₁₄ = −8.166E−09, A₁₆ =−1.513E−09 Twelfth Surface k = 0.000, A₄ = −2.321E−03, A₆ = −1.480E−04,A₈ = 1.069E−05, A₁₀ = 5.462E−08, A₁₂ = −1.313E−08, A₁₄ = 4.805E−10, A₁₆= −2.217E−11 Thirteenth Surface k = 0.000, A₄ = −5.114E−03, A₆ =9.282E−05, A₈ = −4.615E−06, A₁₀ = −1.475E−08, A₁₂ = 1.042E−08, A₁₄ =−8.901E−11, A₁₆ = −1.395E−11 Fourteenth Surface k = 0.000, A₄ =−1.462E−02, A₆ = 5.096E−04, A₈ = −6.553E−06, A₁₀ = 2.050E−08, A₁₂ =−1.745E−08, A₁₄ = −7.332E−10, A₁₆ = 6.119E−11 Fifteenth Surface k =−3.374, A₄ = −8.463E−03, A₆ = 4.184E−04, A₈ = −1.373E−05, A₁₀ =1.279E−07, A₁₂ = 1.100E−08, A₁₄ = −5.270E−10, A₁₆ = 7.656E−12f1=16.65 mmf2=−11.40 mmf3=9.63 mmf4=66.37 mmf5=54.86 mmf6=−30.56 mmf7=−38.90 mmf45=29.54 mmf67=16.33 mmThe values of the respective conditional expressions are as follows:f3/f1=0.58f2/f3=−1.18f4/f=5.97f45/f=2.66f45/f67=−1.81D34/f=0.09D56/f=0.16f7/f=−3.50f2/f1=−0.68f6/f7=0.79

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 13.46 mm, and downsizing ofthe imaging lens is attained.

FIG. 5 shows a lateral aberration that corresponds to the image heightratio H of the imaging lens, and FIG. 6 shows a spherical aberration(mm), astigmatism (mm), and a distortion (%), respectively, of theimaging lens of Numerical Data Example 2. As shown in FIGS. 5 and 6,according to the imaging lens of Numerical Data Example 2, theaberrations are also satisfactorily corrected.

Numerical Data Example 3

Basic data are shown below.

f=9.16 mm, Fno=2.2, ω=33.6°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 4.6861.560 1.5346 56.1 (=νd1)  2* 44.083 −0.003    3 (Stop) ∞ 0.105  4* 9.8920.859 1.6355 24.0 (=νd2)  5* 5.248 0.157  6* 9.581 0.717 1.5346 56.1(=νd3)  7* −35.654 0.786 (=D34)  8* −4.605 0.788 1.5346 56.1 (=νd4)  9*−4.271 0.030 10* −12.412 1.699 1.6355 24.0 (=νd5) 11* −10.957 0.942(=D56) 12* 9.961 0.965 1.6355 24.0 (=νd6) 13* 5.142 0.623 14* 5.8911.292 1.5346 56.1 (=νd7) 15* 3.732 0.700 16 ∞ 0.300 1.5168 64.2 17 ∞0.400 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −5.228E−04, A₆ = 5.257E−05, A₈ = −7.167E−05, A₁₀ = 6.642E−06, A₁₂ =−2.064E−07, A₁₄ = −1.718E−08, A₁₆ = −3.672E−09 Second Surface k = 0.000,A₄ = 1.706E−02, A₆ = −1.665E−02, A₈ = 5.716E−03, A₁₀ = −9.533E−04, A₁₂ =4.016E−05, A₁₄ = 9.227E−06, A₁₆ = −1.010E−06 Fourth Surface k = 0.000,A₄ = 1.824E−02, A₆ = −2.073E−02, A₈ = 7.501E−03, A₁₀ = −1.362E−03, A₁₂ =8.090E−05, A₁₄ = 1.019E−05, A₁₆ = −1.349E−06 Fifth Surface k = 0.000, A₄= 1.418E−02, A₆ = −1.191E−02, A₈ = 2.763E−03, A₁₀ = −3.305E−04, A₁₂ =9.678E−06, A₁₄ = 1.516E−06, A₁₆ = −3.088E−08 Sixth Surface k = 0.000, A₄= 1.439E−02, A₆ = −7.365E−03, A₈ = 1.463E−03, A₁₀ = −1.649E−04, A₁₂ =9.715E−06, A₁₄ = 3.826E−07, A₁₆ = −5.052E−08 Seventh Surface k = 0.000,A₄ = −4.115E−03, A₆ = −4.089E−04, A₈ = 2.326E−04, A₁₀ = −1.364E−05, A₁₂= −4.022E−07, A₁₄ = −3.544E−07, A₁₆ = 2.426E−10 Eighth Surface k =0.000, A₄ = −8.156E−03, A₆ = 7.335E−04, A₈ = 1.820E−04, A₁₀ =−3.874E−05, A₁₂ = 9.548E−08, A₁₄ = 2.413E−07, A₁₆ = 3.202E−08 NinthSurface k = 0.000, A₄ = −3.284E−03, A₆ = 1.711E−04, A₈ = −3.665E−05, A₁₀= −1.211E−06, A₁₂ = −1.670E−06, A₁₄ = 1.315E−07, A₁₆ = 3.488E−08 TenthSurface k = 0.000, A₄ = −3.774E−03, A₆ = −1.071E−03, A₈ = −1.090E−04,A₁₀ = −1.136E−06, A₁₂ = −1.366E−06, A₁₄ = −6.579E−08, A₁₆ = −7.522E−09Eleventh Surface k = 0.000, A₄ = −1.977E−03, A₆ = −3.375E−04, A₈ =5.840E−06, A₁₀ = −9.285E−07, A₁₂ = 9.105E−08, A₁₄ = 7.992E−09, A₁₆ =1.009E−11 Twelfth Surface k = 0.000, A₄ = −5.918E−03, A₆ = −1.970E−05,A₈ = 2.285E−06, A₁₀ = 2.484E−07, A₁₂ = 6.113E−09, A₁₄ = 6.331E−10, A₁₆ =−6.092E−11 Thirteenth Surface k = 0.000, A₄ = −7.396E−03, A₆ =8.056E−05, A₈ = 2.029E−06, A₁₀ = −9.873E−08, A₁₂ = 3.717E−09, A₁₄ =−5.325E−11, A₁₆ = −5.178E−12 Fourteenth Surface k = 0.000, A₄ =−1.274E−02, A₆ = 4.084E−04, A₈ = −7.883E−07, A₁₀ = 4.755E−08, A₁₂ =−4.159E−09, A₁₄ = −4.673E−10, A₁₆ = 1.490E−11 Fifteenth Surface k =−4.383, A₄ = −5.567E−03, A₆ = 2.400E−04, A₈ = −9.162E−06, A₁₀ =1.827E−07, A₁₂ = 9.388E−09, A₁₄ = −5.768E−10, A₁₆ = 8.323E−12f1=9.67 mmf2=−18.95 mmf3=14.20 mmf4=60.48 mmf5=101.17 mmf6=−18.14 mmf7=−24.06 mmf45=38.45 mmf67=−9.69 mmThe values of the respective conditional expressions are as follows:f3/f1=1.47f2/f3=−1.33f4/f=6.60f45/f=4.20f45/f67=−3.97D34/f=0.09D56/f=0.10f7/f=−2.63f2/f1=−1.96f6/f7=0.75

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 11.82 mm, and downsizing ofthe imaging lens is attained.

FIG. 8 shows a lateral aberration that corresponds to the image heightratio H of the imaging lens, and FIG. 9 shows a spherical aberration(mm), astigmatism (mm), and a distortion (%), respectively in theimaging lens of Numerical Data Example 3. As shown in FIGS. 8 and 9,according to the imaging lens of Numerical Data Example 3, theaberrations are also satisfactorily corrected.

Numerical Data Example 4

Basic data are shown below.

f=11.52 mm, Fno=2.8, ω=27.9°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 5.1171.025 1.5346 56.1 (=νd1)  2* −53.792 −0.065    3 (Stop) ∞ 0.121  4*33.647 0.385 1.6355 24.0 (=νd2)  5* 6.316 0.111  6* 11.172 0.746 1.534656.1 (=νd3)  7* 261.521 0.961 (=D34)  8* −4.905 1.202 1.5346 56.1 (=νd4) 9* −4.564 0.100 10* −63.334 1.035 1.6355 24.0 (=νd5) 11* −18.755 2.149(=D56) 12* 8.382 1.036 1.6355 24.0 (=νd6) 13* 5.211 1.755 14* 7.2750.599 1.5346 56.1 (=νd7) 15* 4.224 0.700 16 ∞ 0.300 1.5168 64.2 17 ∞1.259 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −2.207E−03, A₆ = −6.989E−05, A₈ = −7.646E−05, A₁₀ = 6.537E−06, A₁₂ =−4.816E−07, A₁₄ = −8.199E−08, A₁₆ = 3.638E−09 Second Surface k = 0.000,A₄ = 1.851E−02, A₆ = −1.657E−02, A₈ = 5.668E−03, A₁₀ = −9.618E−04, A₁₂ =3.914E−05, A₁₄ = 9.359E−06, A₁₆ = −9.285E−07 Fourth Surface k = 0.000,A₄ = 2.025E−02, A₆ = −2.097E−02, A₈ = 7.489E−03, A₁₀ = −1.365E−03, A₁₂ =7.992E−05, A₁₄ = 1.014E−05, A₁₆ = −1.285E−06 Fifth Surface k = 0.000, A₄= 1.323E−02, A₆ = −1.195E−02, A₈ = 2.773E−03, A₁₀ = −3.309E−04, A₁₂ =9.229E−06, A₁₄ = 1.525E−06, A₁₆ = 2.021E−08 Sixth Surface k = 0.000, A₄= 1.386E−02, A₆ = −7.321E−03, A₈ = 1.465E−03, A₁₀ = −1.613E−04, A₁₂ =1.051E−05, A₁₄ = 4.523E−07, A₁₆ = −7.458E−08 Seventh Surface k = 0.000,A₄ = −4.107E−03, A₆ = −6.095E−04, A₈ = 2.313E−04, A₁₀ = −1.564E−05, A₁₂= −1.063E−06, A₁₄ = −4.057E−07, A₁₆ = 1.971E−08 Eighth Surface k =0.000, A₄ = −7.452E−03, A₆ = 2.441E−04, A₈ = 1.544E−04, A₁₀ =−4.022E−05, A₁₂ = −1.261E−07, A₁₄ = 2.097E−07, A₁₆ = 2.056E−08 NinthSurface k = 0.000, A₄ = −1.153E−03, A₆ = 4.274E−04, A₈ = −1.137E−05, A₁₀= 5.141E−07, A₁₂ = −1.679E−06, A₁₄ = 6.825E−08, A₁₆ = 2.075E−08 TenthSurface k = 0.000, A₄ = −2.008E−03, A₆ = −5.326E−04, A₈ = −6.927E−05,A₁₀ = 3.698E−06, A₁₂ = −9.083E−07, A₁₄ = −2.415E−08, A₁₆ = 2.387E−09Eleventh Surface k = 0.000, A₄ = −2.664E−03, A₆ = −4.928E−04, A₈ =6.485E−06, A₁₀ = −1.390E−06, A₁₂ = 2.179E−08, A₄ = 2.943E−09, A₁₆ =2.577E−11 Twelfth Surface k = 0.000, A₄ = −7.128E−03, A₆ = −1.704E−06,A₈ = −2.063E−06, A₁₀ = 3.368E−07, A₁₂ = 1.676E−08, A₁₄ = 5.661E−10, A₁₆= −9.290E−11 Thirteenth Surface k = 0.000, A₄ = −7.959E−03, A₆ =1.161E−04, A₈ = 1.846E−06, A₁₀ = −1.411E−07, A₁₂ = 2.493E−09, A₁₄ =−4.883E−11, A₁₆ = −1.244E−12 Fourteenth Surface k = 0.000, A₄ =−1.477E−02, A₆ = 4.361E−04, A₈ = 2.104E−07, A₁₀ = 9.535E−08, A₁₂ =−2.529E−09, A₁₄ = −4.606E−10, A₁₆ = 1.104E−11 Fifteenth Surface k =−5.017, A₄ = −8.878E−03, A₆ = 3.107E−04, A₈ = −7.809E−06, A₁₀ =1.765E−07, A₁₂ = 8.693E−09, A₁₄ = −5.836E−10, A₁₆ = 8.814E−12f1=8.79 mmf2=−12.30 mmf3=21.81 mmf4=55.06 mmf5=41.55 mmf6=−24.82 mmf7=−20.22 mmf45=22.80 mmf67=−10.77 mmThe values of the respective conditional expressions are as follows:f3/f1=2.48f2/f3=−0.56f4/f=4.78f45/f=1.98f45/f67=−2.12D34/f=0.08D56/f=0.19f7/f=−1.76f2/f1=−1.40f6/f7=1.23

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 13.32 mm, and downsizing ofthe imaging lens is attained.

FIG. 11 shows a lateral aberration that corresponds to the image heightratio H of the imaging lens, and FIG. 12 shows a spherical aberration(mm), astigmatism (mm), and a distortion (%), respectively, of theimaging lens of Numerical Data Example 4. As shown in FIGS. 11 and 12,according to the imaging lens of Numerical Data Example 4, theaberrations are also satisfactorily corrected.

Numerical Data Example 5

Basic data are shown below.

f=8.67 mm, Fno=2.2, ω=35.1°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 4.7681.225 1.5346 56.1 (=νd1)  2* 13.787 0.006  3 (Stop) ∞ 0.121  4* 9.1121.131 1.6355 24.0 (=νd2)  5* 5.264 0.174  6* 6.739 0.562 1.5346 56.1(=νd3)  7* −18.422 0.894 (=D34)  8* −4.360 1.120 1.5346 56.1 (=νd4)  9*−4.203 0.023 10* −13.261 1.306 1.6355 24.0 (=νd5) 11* −11.418 0.915(=D56) 12* 9.779 1.044 1.6355 24.0 (=νd6) 13* 5.107 0.545 14* 6.0501.172 1.5346 56.1 (=νd7) 15* 3.667 0.680 16 ∞ 0.300 1.5168 64.2 17 ∞0.392 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −1.442E−04, A₆ = −4.252E−04, A₈ = −5.829E−05, A₁₀ = 7.729E−06, A₁₂ =−7.729E−07, A₁₄ = −2.721E−07, A₁₆ = 2.173E−08 Second Surface k = 0.000,A₄ = 1.225E−02, A₆ = −1.770E−02, A₈ = 5.696E−03, A₁₀ = −8.952E−04, A₁₂ =4.534E−05, A₁₄ = 5.387E−06, A₁₆ = −6.549E−07 Fourth Surface k = 0.000,A₄ = 1.248E−02, A₆ = −2.005E−02, A₈ = 7.570E−03, A₁₀ = −1.470E−03, A₁₂ =1.137E−04, A₁₄ = 1.042E−05, A₁₆ = −1.989E−06 Fifth Surface k = 0.000, A₄= 4.826E−03, A₆ = −1.017E−02, A₈ = 2.627E−03, A₁₀ = −3.251E−04, A₁₂ =9.698E−06, A₁₄ = 1.282E−06, A₁₆ = −3.440E−08 Sixth Surface k = 0.000, A₄= 3.529E−03, A₆ = −7.102E−03, A₈ = 1.423E−03, A₁₀ = −1.676E−04, A₁₂ =1.021E−05, A₁₄ = 5.379E−07, A₁₆ = −5.165E−09 Seventh Surface k = 0.000,A₄ = −3.710E−03, A₆ = −2.157E−04, A₈ = 2.360E−04, A₁₀ = −5.668E−06, A₁₂= 1.774E−07, A₁₄ = 1.109E−07, A₁₆ = 3.634E−08 Eighth Surface k = 0.000,A₄ = −3.150E−03, A₆ = 1.430E−03, A₈ = 1.997E−04, A₁₀ = −3.485E−05, A₁₂ =−3.109E−07, A₁₄ = 2.738E−07, A₁₆ = 1.097E−08 Ninth Surface k = 0.000, A₄= −3.571E−03, A₆ = 2.703E−04, A₈ = −1.163E−05, A₁₀ = 1.381E−06, A₁₂ =−1.482E−06, A₁₄ = −2.457E−08, A₁₆ = 1.603E−08 Tenth Surface k = 0.000,A₄ = −7.473E−03, A₆ = −8.908E−04, A₈ = −1.243E−04, A₁₀ = 5.264E−06, A₁₂= −5.447E−07, A₁₄ = −1.393E−07, A₁₆ = 2.669E−08 Eleventh Surface k =0.000, A₄ = −3.477E−03, A₆ = −4.574E−04, A₈ = 1.270E−05, A₁₀ =7.131E−08, A₁₂ = 1.551E−07, A₁₄ = 2.009E−08, A₁₆ = −1.129E−09 TwelfthSurface k = 0.000, A₄ = −7.052E−03, A₆ = 3.262E−05, A₈ = 4.109E−06, A₁₀= 3.024E−07, A₁₂ = 2.279E−09, A₁₄ = −2.325E−10, A₁₆ = −1.801E−11Thirteenth Surface k = 0.000, A₄ = −7.766E−03, A₆ = 1.105E−04, A₈ =−3.842E−07, A₁₀ = −9.066E−08, A₁₂ = 5.815E−09, A₁₄ = −4.823E−11, A₁₆ =−5.462E−12 Fourteenth Surface k = 0.000, A₄ = −1.216E−02, A₆ =3.947E−04, A₈ = −1.379E−06, A₁₀ = 3.881E−08, A₁₂ = −3.941E−09, A₁₄ =−4.418E−10, A₁₆ = 1.538E−11 Fifteenth Surface k = −3.754, A₄ =−6.588E−03, A₆ = 3.515E−04, A₈ = −1.117E−05, A₁₀ = 1.138E−07, A₁₂ =1.115E−08, A₁₄ = −5.171E−10, A₁₆ = 6.563E−12f1=13.02 mmf2=−22.14 mmf3=9.30 mmf4=62.66 mmf5=101.37 mmf6=−18.42 mmf7=−21.01 mmf45=38.47 mmf67=−9.32 mmThe values of the respective conditional expressions are as follows:f3/f1=0.71f2/f3=−2.38f4/f=7.23f45/f=4.44f45/f67=−4.13D34/f=0.10D56/f=0.11f7/f=−2.42f2/f1=−1.70f6/f7=0.88

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 11.51 mm, and downsizing ofthe imaging lens is attained.

FIG. 14 shows a lateral aberration that corresponds to the image heightratio H of the imaging lens, and FIG. 15 shows a spherical aberration(mm), astigmatism (mm), and a distortion (%), respectively, of theimaging lens of Numerical Data Example 5. As shown in FIGS. 14 and 15,according to the imaging lens of Numerical Data Example 5, theaberrations are also satisfactorily corrected.

Numerical Data Example 6

Basic data are shown below.

f=8.40 mm, Fno=2.2, ω=36.0°

Unit: mm Surface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 7.6581.100 1.5346 56.1 (=νd1)  2* −53.073 −0.069    3 (Stop) ∞ 0.106  4*16.879 0.380 1.6355 24.0 (=νd2)  5* 6.417 0.076  6* 9.768 0.933 1.534656.1 (=νd3)  7* −10.747 2.035 (=D34)  8* −3.282 0.515 1.5346 56.1 (=νd4) 9* −3.135 0.030 10* −49.303 0.923 1.6355 24.0 (=νd5) 11* −27.983 0.694(=D56) 12* 8.841 1.211 1.6355 24.0 (=νd6) 13* 5.141 0.767 14* 5.5211.198 1.5346 56.1 (=νd7) 15* 3.529 0.680 16 ∞ 0.300 1.5168 64.2 17 ∞0.418 (Image ∞ plane) Aspheric Surface Data First Surface k = 0.000, A₄= −4.156E−03, A₆ = −5.223E−05, A₈ = −5.968E−05, A₁₀ = 1.006E−05, A₁₂ =6.018E−08, A₁₄ = −3.837E−08, A₁₆ = −6.205E−09 Second Surface k = 0.000,A₄ = 1.712E−02, A₆ = −1.648E−02, A₈ = 5.700E−03, A₁₀ = −9.584E−04, A₁₂ =3.864E−05, A₁₄ = 9.170E−06, A₁₆ = −9.202E−07 Fourth Surface k = 0.000,A₄ = 1.915E−02, A₆ = −2.128E−02, A₈ = 7.442E−03, A₁₀ = −1.369E−03, A₁₂ =7.994E−05, A₁₄ = 1.026E−05, A₁₆ = −1.252E−06 Fifth Surface k = 0.000, A₄= 1.316E−02, A₆ = −1.210E−02, A₈ = 2.743E−03, A₁₀ = −3.303E−04, A₁₂ =1.025E−05, A₁₄ = 1.712E−06, A₁₆ = 1.496E−08 Sixth Surface k = 0.000, A₄= 1.443E−02, A₆ = −7.325E−03, A₈ = 1.468E−03, A₁₀ = −1.653E−04, A₁₂ =9.429E−06, A₁₄ = 3.314E−07, A₁₆ = −5.385E−08 Seventh Surface k = 0.000,A₄ = −2.920E−03, A₆ = −6.142E−04, A₈ = 2.006E−04, A₁₀ = −1.681E−05, A₁₂= −5.885E−07, A₁₄ = −3.186E−07, A₁₆ = 1.411E−08 Eighth Surface k =0.000, A₄ = −5.868E−03, A₆ = 4.981E−04, A₈ = 1.644E−04, A₁₀ =−3.745E−05, A₁₂ = 3.196E−07, A₁₄ = 2.464E−07, A₁₆ = 1.890E−08 NinthSurface k = 0.000, A₄ = −2.778E−03, A₆ = 5.034E−04, A₈ = −1.365E−06, A₁₀= 3.204E−07, A₁₂ = −1.817E−06, A₁₄ = 6.919E−08, A₁₆ = 2.640E−08 TenthSurface k = 0.000, A₄ = −2.145E−03, A₆ = −7.136E−04, A₈ = −7.507E−05,A₁₀ = 4.838E−06, A₁₂ = −8.803E−07, A₁₄ = −5.411E−08, A₁₆ = −3.818E−09Eleventh Surface k = 0.000, A₄ = −1.111E−03, A₆ = −4.709E−04, A₈ =1.734E−06, A₁₀ = −1.459E−06, A₁₂ = 5.712E−08, A₁₄ = 7.257E−09, A₁₆ =2.782E−10 Twelfth Surface k = 0.000, A₄ = −4.802E−03, A₆ = 2.466E−05, A₈= −1.921E−07, A₁₀ = 1.754E−07, A₁₂ = 5.647E−09, A₁₄ = 6.112E−10, A₁₆ =−6.960E−11 Thirteenth Surface k = 0.000, A₄ = −6.235E−03, A₆ =6.105E−05, A₈ = 2.172E−06, A₁₀ = −1.096E−07, A₁₂ = 3.182E−09, A₁₄ =−5.783E−11, A₁₆ = −4.904E−12 Fourteenth Surface k = 0.000, A₄ =−1.286E−02, A₆ = 4.059E−04, A₈ = −7.829E−07, A₁₀ = 4.146E−08, A₁₂ =−4.337E−09, A₁₄ = −4.785E−10, A₁₆ = 1.473E−11 Fifteenth Surface k =−3.781, A₄ = −5.334E−03, A₆ = 2.322E−04, A₈ = −9.022E−06, A₁₀ =1.882E−07, A₁₂ = 9.396E−09, A₁₄ = −5.765E−10, A₁₆ = 8.140E−12f1=12.60 mmf2=−16.52 mmf3=9.73 mmf4=59.00 mmf5=100.14 mmf6=−22.14 mmf7=−23.14 mmf45=36.69 mmf67=−10.76 mmThe values of the respective conditional expressions are as follows:f3/f1=0.77f2/f3=−1.70f4/f=7.02f45/f=4.37f45/f67=−3.41D34/f=0.24D56/f=0.08f7/f=−2.75f2/f1=−1.31f6/f7=0.96

Accordingly, the imaging lens of Numerical Data Example 6 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (length without the filter 10) is 11.19 mm, and downsizing ofthe imaging lens is attained.

FIG. 17 shows a lateral aberration that corresponds to the image heightratio H of the imaging lens, and FIG. 18 shows a spherical aberration(mm), astigmatism (mm), and a distortion (%), respectively, of theimaging lens of Numerical Data Example 6. As shown in FIGS. 17 and 18,according to the imaging lens of Numerical Data Example 6, theaberrations are also satisfactorily corrected.

According to the imaging lens of the embodiment described above, it isachievable to have a wide angle of view (2ω) of 70° or greater.According to Numerical Data Examples 1 to 6, the imaging lenses havewide angles of view of 54.2° to 72.0°. According to the imaging lens ofthe embodiment, it is possible to take an image over a wider range thanthat taken by a conventional imaging lens.

Moreover, in these years, with advancement in digital zoom technology,which enables to enlarge any area of an image obtained through animaging lens by image processing, an imaging element having a high pixelcount is often used in combination with a high resolution imaging lens.In case of such an imaging element with a high pixel count, alight-receiving area of each pixel decreases, so that an image takentends to be dark. As a method for correcting this problem, there is amethod of enhancing light-receiving sensitivity of the imaging elementusing an electrical circuit. However, when the light-receivingsensitivity increases, a noise component that does not directlycontribute to image formation is also amplified, so that it is necessaryto use another circuit for reducing the noise. According to the imaginglenses of Numerical Data Examples 1 to 6, the Fnos are as small as 2.2to 2.9. According to the imaging lens of the embodiment, it is possibleto obtain a sufficiently bright image without the above-describedelectrical circuit.

Accordingly, when the imaging lens of the embodiment or the imagingdevice equipped with the imaging lens is mounted in cellular phones,smartphones, digital still cameras, portable information terminals,security cameras, onboard cameras, and network cameras, it is possibleto attain both high performance and downsizing of the cameras.

The present invention is applicable in an imaging lens to be mounted ina relatively small camera for portable devices including cellularphones, smartphones, and portable information terminals, digital stillcameras, security cameras, onboard cameras, and network cameras.

The disclosure of Japanese Patent Application No. 2014-038093, filed onFeb. 28, 2014, is incorporated in the application by reference.

While the present invention has been explained with reference to thespecific embodiment of the present invention, the explanation isillustrative and the present invention is limited only by the appendedclaims.

What is claimed is:
 1. An imaging lens comprising: a first lens grouphaving positive refractive power; a second lens group having positiverefractive power; and a third lens group having negative refractivepower, arranged in this order from an object side to an image planeside, wherein said first lens group includes a first lens havingpositive refractive power, a second lens having negative refractivepower, and a third lens having positive refractive power, said secondlens group includes a fourth lens having positive refractive power and afifth lens having positive refractive power, said third lens groupincludes a sixth lens and a seventh lens, and said first lens has anAbbe's number νd1, said second lens has an Abbe's number νd2, said thirdlens has an Abbe's number νd3, said fourth lens has an Abbe's numberνd4, and said fifth lens has an Abbe's number νd5 so that the followingconditional expressions are satisfied:40<νd1<75,20<νd2<35,40<νd3<75,40<νd4<75,20<νd5<35.
 2. The imaging lens according to claim 1, wherein said sixthlens has negative refractive power, said seventh lens has negativerefractive power, and said sixth lens has an Abbe's number νd6 and saidseventh lens has an Abbe's number νd7 so that the following conditionalexpressions are satisfied:20<νd6<3540<νd7<75.
 3. The imaging lens according to claim 1, wherein said firstlens has a focal length f1, and said third lens has a focal length f3 sothat the following conditional expression is satisfied:0.3<f3/f1<3.0.
 4. The imaging lens according to claim 1, wherein saidsecond lens has a focal length f2, and said third lens has a focallength f3 so that the following conditional expression is satisfied:−3.0<f2/f3<−0.3.
 5. The imaging lens according to claim 1, wherein saidfourth lens has a focal length f4 so that the following conditionalexpression is satisfied:4.5<f4/f<9.0 where f is a focal length of a whole lens system.
 6. Theimaging lens according to claim 1, wherein said fourth lens and saidfifth lens have a composite focal length f45 so that the followingconditional expression is satisfied:1.5<f45/f<5.0 where f is a focal length of a whole lens system.
 7. Theimaging lens according to claim 1, wherein said fifth lens is disposedaway from said sixth lens by a distance D56 on an optical axis thereofso that the following conditional expression is satisfied:0.05<D56/f<0.25 where f is a focal length of a whole lens system.
 8. Theimaging lens according to claim 1, wherein said seventh lens has a focallength f7 so that the following conditional expression is satisfied:−4.0<f7/f<−1.0 where f is a focal length of a whole lens system.